Television cameras for infrared imaging, utilizing a Vidicon tube having a pyroelectric target such as triglycine sulphate are well-known. These cameras form an image by sensing the thermal differences in the scenes before them. The image transmitted by the television camera decays and disappears unless the objects being viewed are constantly moving with respect to the camera target since the heat produced is dissipated at a rapid rate. Prior art devices overcome this difficulty by constantly panning slowly moving scenes, by chopping the entrant light beam or by mechanically orbiting an eccentrically mounted planar wedge or lens carried within the camera so that the image received by the camera is constantly in motion. Such prior art devices are not entirely satisfactory.
Panning or moving the target with a cyclic vibratory motion does not give continuous results since the target must come to a momentary stop at each end of the movement.
A difficulty with prior known mechanical orbiting devices is that the mechanical means employed vibrates the assembly and thereby degrades the thermal image. Another difficulty with such orbiting devices is that their orbiting mechanisms can only work at a fixed speed of rotation. In the present invention, image clarity is improved by varying the speed of rotation of a planar, angularly disposed light transmitting plate to complement the motion in the scene being viewed. A synchronous D. C. motor and an elastomeric belt connected between the motor and the plate is employed to minimize microphonic disturbances.
The present invention rotates the image in a small circular path and produces no more disturbances than if only the trace shadows were rotating. It is simple and easy to install in any infrared camera and does not have any of the disadvantages of the compensating orbiters. The present invention operates with a variable speed control and can be adjusted to the optimum image conditions. Because of its simplicity, it is practically free of repair.